U.S. patent number 4,672,493 [Application Number 06/727,220] was granted by the patent office on 1987-06-09 for thin-film magnetic head with a double gap for a recording medium to be magnetized vertically.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Herbert Schewe.
United States Patent |
4,672,493 |
Schewe |
June 9, 1987 |
Thin-film magnetic head with a double gap for a recording medium to
be magnetized vertically
Abstract
A thin-film magnetic head with a layer-wise build-up on a
nonmagnetic substrate for a recording medium which can be
magnetized vertically comprises a magnetic conduction body carrying
the magnetic flux, with two outer magnet legs and a further central
magnet leg, the poles of which facing the recording medium are
arranged one behind the other as seen in the direction of motion of
the head, and with predetermined gap widths between each other,
where the current conductors of a write/read coil arrangement
extend through spaces formed between the central magnet leg and a
respective outer magnet leg adjacent thereto. With this magnetic
head it is possible to generate a magnetic writing field, the field
pattern of which has a pronounced largely symmetrical maximum. It
is provided that the current conductors of the coil arrangement
also run through a further space where the current flow directions
in the current conductors arranged on both sides of the central
magnet leg are opposed to each other. It is particularly
advantageous if the central magnet leg has, at least in the
vicinity of the pole, a higher saturation magnetization than the
outer magnet legs, so that these magnet legs are in magnetic
saturation sooner than the central leg during writing.
Inventors: |
Schewe; Herbert
(Herzogenaurach, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin and Munich, DE)
|
Family
ID: |
25820896 |
Appl.
No.: |
06/727,220 |
Filed: |
April 25, 1985 |
Foreign Application Priority Data
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May 4, 1984 [DE] |
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3416544 |
Jan 21, 1985 [DE] |
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3501810 |
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Current U.S.
Class: |
360/125.15;
360/122; 360/123.11; 360/125.17; G9B/5.044 |
Current CPC
Class: |
G11B
5/1278 (20130101) |
Current International
Class: |
G11B
5/127 (20060101); G11B 005/187 (); G11B
005/127 () |
Field of
Search: |
;360/125,110,113,119,121-123,126-127 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0012910 |
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Jul 1980 |
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EP |
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0012912 |
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Jul 1980 |
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EP |
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0078374 |
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May 1983 |
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EP |
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0088812 |
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May 1983 |
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JP |
|
Other References
Valstyn, "Composite Read/Write Recording Head", IBM TDB, Sep. 1971,
vol. 14, No. 4, pp. 1283-1284. .
Hoagland, "Combined Longitudinal and Vertical Magnetic Recording
Head", IBM TDB, Jan. 1978, vol. 20, No. 8, pp. 3311-3312. .
IEEE Transactions on Magnetics: vol. MAG-16, No. 1, Jan. 1980, pp.
71-76, vol. MAG-17, No. 6, Nov. 1981, pp. 3120-3122, vol. MAG-18,
No. 6, Nov. 1982, pp. 1158-1163. .
Feinwerktechnik & Messtechnik, vol. 88, No. 2, Mar. 1980, pp.
53-59, Siemens-Zeitschrift, vol. 52, No. 7, 1978, pp.
434-437..
|
Primary Examiner: Hecker; Stuart N.
Assistant Examiner: Severin; David J.
Attorney, Agent or Firm: Kenyon & Kenyon
Claims
What is claimed is:
1. A thin-film magnetic head produced by a stratified build-up on a
nonmagnetic substrate for a recording medium having a magnetizable
storage layer into which information can bve written along a track
by vertical magnetization, the magnetic head comprising:
a magnetic conduction body for carrying magnetic flux, the body
having two outer magnet legs and a further cental magnet leg, each
magnet leg having a pole facing the recording medium and being
arranged one behind the other as viewed in the direction of
relative motion of the head and medium and having predetermined gap
widths between adjacent poles, said magnet legs being shaped so as
to form enlarged spaces between each other at a location spaced
away from the poles;
a write/read coil arrangement having current conductors extending
through one of the spaces formed between the central magnet leg and
one of the outer magnet legs adjacent thereto, the current
conductors of the coil arrangement further extending through the
other space between the central magnet leg and the other of the
outer magnet legs, the current flow directions in the current
conductors arranged on both sides of the central magnet leg being
opposed to each other so that during writing into said recording
medium, a magnetic writing field is generated which is
substantially symmetrical with respect to a plane extending
vertically to the recording medium through the pole of the central
magnet leg.
2. The magnetic head recited in claim 1, wherein the magnetic
conduction body comprises at least partially a magnetically soft
material.
3. The magnetic head recited in claim 1, wherein the magnetic
conduction body comprises a material, the easy magnetization of
which is aligned at least largely perpendicularly to the conduction
direction of the magnetic flux.
4. The magnetic head recited in claim 1, wherein the magnetic
conduction body comprises a material, the relative permeability of
which is at least 1500 and preferably at least 2000.
5. The magnetic head recited in claim 1, wherein the poles of the
magnet legs adjacent to the central magnet leg have a substantially
larger dimension in the direction of motion of the magnetic head
than the magnetic pole of the central magnet leg.
6. The magnetic head recited in claim 1, wherein the coil
arrangement is formed by at least largely planar coil windings.
7. The magnetic head recited in claim 1, wherein the coil
arrangement comprises a coil winding disposed around the central
magnet leg.
8. The magnetic head recited in claim 1, wherein the two magnet
legs adjacent to the central magnet leg each have a predetermined
small cross section in a partial section, so that these partial
sections are driven, at least largely, into magnetic saturation by
a write current of the coil arrangement.
9. The magnetic head recited in claim 8, wherein the partial
sections with predetermined small cross section of the two magnet
legs adjacent to the central magnet leg also include the magnet
poles of these magnet legs.
10. The magnetic head recited in claim 1, wherein the central
magnet leg comprises, at least in the region of its pole, a
material having a saturation magnetization which has a higher value
than a saturation magnetization of the material of the outer magnet
legs at least in the region of their poles, so that the outer
magnet legs are driven by a write current flowing in the coil
arrangement substantially into magnetic saturation sooner than the
central magnet leg.
11. The magnetic head recited in claim 10, wherein the saturation
magnetization of the central magnet leg at least in the region of
its pole, is at least 20% and preferably at least 30% higher than
the saturation magnetization of the outer magnet legs at least in
the region of their poles.
12. The magnetic head recited in claim 10, wherein, for the parts
of the magnetic conduction body of the material with the
comparatively lower saturation magnetization, a material with a
saturation magnetization of less than 8 kA/cm and preferably less
than 5 kA/cm is provided.
13. The magnetic head recited in claim 10, wherein, for the parts
of the magnetic conduction body comprising the material with the
relatively higher saturation magnetization, a material with a
saturation magnetization of at least 10 kA/cm and preferably more
than 11 kA/cm is provided.
14. The magnetic head recited in claim 10, wherein the material
with the lower saturation magnetization comprises a permalloy
alloy.
15. The magnetic head recited in claim 10, wherein the material
with the higher saturation magnetization consists of one of an CoZr
alloy, an FeB alloy and an FeSiRu alloy.
16. The magnetic head recited in claim 10, wherein at least one of
the two outer magnet legs comprises a first magnetic layer having
relatively low saturation magnetization and further has outside of
the region of its pole at least one further magnetic layer, the
saturation magnetization of which is higher than the lower
saturation magnetization of the first magnetic layer of the
leg.
17. The magnetic head recited in claim 16, wherein the further
magnetic layer has a saturation magnetization which is at least 20%
and preferably at least 30% higher than the saturation
magnetization of the first magnetic layer.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a thin-film magnetic head with a
layer-wise build-up on a nonmagnetic substrate for a recording
medium which contains a magnetizable storage layer, into which
information can be written along a track by perpendicular
(vertical) magnetization. The magnetic head comprises a magnetic
conducting body for carrying the magnetic flux, with two outer
magnet legs and a further central magnet leg, wherein the poles of
these magnet legs facing the recording medium, as seen in the
direction of motion of the head, are arranged one behind the other
and with predetermined gap widths between each other. The magnetic
head is further provided with a read/write coil device, the current
conductors of which extend through one of the spaces formed between
the central magnet leg and one each of the adjacent outer magnet
legs. Such a magnet head is known, for instance, from European
Patent application No. 0 078 374 Al.
The principle of vertical magnetization for storing information in
special recording media is generally known (see, for instance,
"IEEE Transactions on Magnetics", vol. MAG-16, No. 1, January 1980,
pages 71 to 76; DE-OS No. 29 24 013 or U.S. Pat. No. 4,278,544;
European Patent Application No. 0 012 910 Al; European Patent
Application No. 0 012 912 Al. The recording media to be provided
for this principle, also called vertical magnetization, may be
present in the form of rigid magnetic discs, flexible individual
discs (floppy discs) or magnetic tape. Such a recording medium has
at least one magnetizable storage layer of predetermined thickness
which contains a magnetically anisotropic material, particularly of
a CoCr alloy. The axis of the so-called easy magnetization of this
layer is oriented perpendicularly to the surface of the medium. By
means of a special magnetic head, the individual pieces of
information can then be written along a track as bits in successive
sections, also called cells or blocks, by appropriate magnetization
of the storage layer. In practice, the magnetic flux changes, i.e.,
the transitions from one magnetization direction to the opposite
one are generally used as the information. The bits have a
predetermined extent, also designated as the wavelength, in the
longitudinal direction of the track. This extent can be
substantially smaller than the limit which exists with storage
according to the known principle of longitudinal (horizontal)
magnetization by the demagnetization. Thus, the information density
in the special recording media can be increased accordingly by
vertical magnetization.
The combined magnetic write and read heads known for the principle
of longitudinal magnetization, i.e., heads with which the write as
well as the read function can be carried out, cannot be used
without problem for vertical magnetization. When using these heads,
which generally have a shape similar to a ring head, although a
magnetic flux conduction also desired with the principle of
vertical magnetization to form a circuit closed as far as possible
with low magnetic resistance can be achieved, it is difficult to
generate a sufficiently strong writing field for high bit densities
and a correspondingly small width of the so-called air gap formed
between the magnetic poles.
One is therefore compelled to develop special magnetic write/read
heads for the principle of vertical magnetization. A head suitable
therefore comprises, in general, a so-called main pole, by which a
sufficiently strong vertical magnetic field for changing the
magnetization of the individual sections of the storage layer is
generated. The necessary magnetic return can then be realized, for
instance, by means of a so-called auxiliary pole which is located,
as far as the recording medium is concerned, for instance, on the
same side as the main pole (see, for instance, "IEEE Trans. Magn."
vol. MAG-17, No. 6, November 1981, pages 3120 to 3122 or vol.
MAG-18, no. 6, November 1982, pages 1158 to 1163; U.S. Pat. No.
4,287,544; European Patent application No. 0 012 912 Al).
In magnetic heads of this head type, the auxiliary pole is to serve
in all cases only for the return of the magnetic flux. A possible
concurrent writing of this pole may possibly be tolerated because
it is always lagging the writing main pole and thereby overwrites
information which may have been written by the auxiliary pole.
However, in order to suppress concurrent reading of the auxiliary
pole with its trailing edge at least to a large extent, the air gap
formed between the two poles would have to be relatively wide in
order to be able to thus ensure a far-reaching reduction of the
magnetic flux density at the auxiliary pole. Gap layers of such
width, however, can be realized in magnetic heads to be built-up by
a thin-film technique only with difficulty.
This technique is generally known (see, for instance,
"Feinwerktechnik und Messtechnik", vol. 88, No. 2, March 1980,
pages 53 to 59, or "Siemens-Zeitschrift", vol. 52, No. 7, 1978,
pages 434 to 437). The magnetic head shown in European Patent
Application No. 0 078 374 Al mentioned at the outset also is to be
manufactured by this technique.
Due to the difficulties arising with respect to concurrent reading
of the auxiliary pole, the magnetic head known from European Patent
Application No. 0 078 374 Al has not only two magnet legs forming a
main and an auxiliary pole, but also a third, central magnet leg
which is arranged between the two outer magnet legs. The ends of
these, therefore, three magnet legs which face the recording medium
and which each form a pole are spaced from each other by a narrow
air gap, so that this magnetic head type is also designated as a
double-gap magnetic head. Through only one of the two magnetic
heads formed between the central magnet leg and a respective outer
magnet leg extend the current conductors of a write and read coil
winding, while the other space is filled with a nonmagnetic
material. With this design of the known magnetic head, it should be
possible to generate for the write function a magnetic field which
has in the vicinity of the pole of the central magnet leg a narrow,
strong maximum of predetermined polarity, while in the adjoining
regions of the poles of the two outer magnet legs, a substantially
wider but only weak maximum with opposite polarity follows. (See
FIG. 4 of this European Patent application). It has been found,
however, that this idealized symmetrical field pattern can hardly
be achieved with this known magnetic head. The magnetic field
formed between the poles of the one outer magnet leg and the
central magnet leg rather is substantially smaller than the
magnetic field of the poles of the central magnet leg and the
other, outer magnet leg. This makes the field heavily asymmetrical
and differs only slightly from the field pattern such as is
generated by known thin-film magnetic heads with ring head-like
shape, for instance, according to European Patent Application No. 0
012 912 Al and is shown in FIG. 3 of European Patent Application EP
0 078 374 Al.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to improve the
known thin-film magnetic head of the type mentioned above in such a
manner that the symmetrical field desired thereby and caused by its
magnet legs is achieved, at least to a large degree.
According to the invention, this problem is solved by the provision
that the current conductors of the coil device run also through the
further space, where the current flow directions in the current
conductors thus arranged on both sides of the central magnet leg
are opposite.
The advantages connected with the embodiment of the thin-film
magnetic head according to the invention are, in particular, that
magnetic field conditions can be set for the write function with
the current conductors of the write/read coil device by the current
conductors extending through the two interspaces, which are at
least approximately symmetrical with respect to a plane extending
through the pole of the central magnet leg perpendicularly to the
recording medium, where a pronounced maximum is formed in the area
of this symmetry plane, i.e., the magnetic head then writes
advantageously the information into the recording medium as a quasi
single-pole head. For the write function, the high efficiency of a
ring head can be achieved because of the good magnetic flux
conduction. Advantageously, the vertical component of the
magnetization is strongly preferred and the level of the read
signal is increased accordingly.
It is particularly advantageous if the central magnet leg
comprises, at least in the vicinity of its pole, a material, the
saturation magnetization of which has a higher value than, by
comparison, the material or materials of the outer magnet legs, at
least in the vicinity of their poles. In this way, the outer magnet
legs in the area of their poles are driven, at least approximately,
into magnetic saturation during the write function due to a write
current flowing in the coil device, while saturation in the central
magnet leg is avoided by relatively small write currents, and
thereby, the maximum attainable magnetic field is reduced
accordingly.
Further advantageous embodiments of the magnetic thin-film head
according to the invention will be apparent from the description
which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail in the following
detailed description with reference to the drawings in which:
FIG. 1 shows an embodiment of a magnetic double-gap head according
to the invention schematically illustrated as a longitudinal
section;
FIG. 2 shows part of the head of FIG. 1 in greater detail; and
FIGS. 3 to 5 show further embodiments of magnetic heads according
to the invention in corresponding views. Like parts are provided
with like reference symbols in the figures.
DETAILED DESCRIPTION
With reference now to the drawings, in the thin-film magnetic head
according to the invention shown in FIG. 1, three-leg embodiments
known per se are taken as a start for the principle of vertical
magnetization (see, for instance, the mentioned European Patent
Application No. 0 078 374 Al). The head, generally designated with
2 which is to be shown, for instance, during its write function, is
located on one flat side of a substrate 3 which forms, for
instance, the end face or the back side of a customary element also
called a flying body, and is indicated only partially in the
figure. This head can be conducted relative to a recording medium M
known per se, which can be magnetized vertically, at a low flying
height f of, for instance, 0.2 .mu.um over a storage layer 4 of
this medium along a track. The storage layer consists, for
instance, of a CoCr alloy which may optionally be placed on a
magnetically soft substrate, for instance, of NiFe. The relative
direction of motion of the recording medium M with respect to the
magnetic head 2 is indicated in the figure by the arrow v.
The magnetic head 2 has three magnet legs 5 to 7 which are oriented
largely and in particular at their ends 8 to 10 facing the
recording medium M and form there respective magnet poles P.sub.1,
P.sub.2 and P.sub.3. Between these three leg ends, two air gaps 11
and 12 are formed with advantageously small longitudinal widths w
and w' pointing in the direction of motion v, of less than 1 .mu.m
and, in particular, less than 0.3 .mu.m. For instance, the widths w
and w' of this double gap have approximately the same size. In a
central region 14 of the magnetic head, the distances between the
individual magnet legs 5 to 7 are enlarged as compared to the
corresponding gap widths w and w' in that, for instance, the outer
magnet leg 5 which is backward with respect to the direction of
motion leads in this region, to a larger distance a relative to the
oentral magnet leg 6. Similarly a distance a' is formed in this
region 14 between the central magnet leg 6 and the inner magnet leg
7 which rests flat on the substrate 3. Outside this region, the
three magnet legs 5 to 7 are brought back together in a manner
known per se in a connecting region 15 on the side facing away from
the recording medium M. The outer and the inner magnet leg 5 and 7
thus form a conducting body 16 carrying the magnetic flux, of ring
head-like shape which in addition is equipped with a central magnet
leg 6 which is surrounded by legs 5 and 7.
For the write and read function, the magnetic head 2 is provided
with a coil device 18 which is formed, according to the embodiment
of FIG. 1, by two single or multilayer flat coil windings 19 and
20. These coil windings, which can be fabricated, for instance, by
a known planar technique, are arranged parallel at least to a large
degree. The current conductors 21 of the planar coil winding 19
facing the substrate 3 extend not only through the space 22 formed
between the inner magnet leg 7 and the central magnet leg 6 in the
region 14, but extend also in the region 23 which follows the
regions 14 and 15 on the side of the magnetic conduction body 16
facing away from the recording medium M. In a similar manner, also
the current conductors 24 of the further coil winding 20 are
brought through a space 25 between the central magnet leg 6 and the
outer magnet leg 5. As is further indicated in the figure by
symbols for the current flow directions, the current flow
directions in the current conductors 21 and 24 of the two coil
windings 19 and 20 are to be antiparallel, according to the
invention. For this purpose the two coil windings are connected in
series. In this manner a magnetic field can be generated in the
vicinity of the pole P.sub.2 of the central magnet leg 6 for the
write function which has a pronounced maximum there, as is typical
of the so-called single-pole heads.
These field relationships are illustrated in greater detail in FIG.
2, in which the end of the magnetic head 2 facing the recording
medium according to FIG. 1 is reproduced enlarged. In FIG. 2, the
magnetizations in the individual legs 5 to 7 are illustrated by
lines with arrows 27 to 29, which are obtained due to the chosen
current flow directions in the current conductors 21 and 24 of the
two coil windings 19 and 20. The field lines issuing at the magnet
pole P.sub.1 to P.sub.3 are indicated by the lines designated with
30. FIG. 2 further shows in a diagram the magnetic base field
H.sub.y which can be generated by the magnetic head and points in
the y-direction as a function of the position plotted on an x-axis
in the relative direction of motion of the magnetic head. As can
further be seen in this figure directly, the width of the ourve
H.sub.y which is at least largely symmetrical to a plane E.sub.s,
extends through the pole P.sub.2 and is perpendicular to the
recording medium and is therefore pointing in the y-direction, can
be influenced by a suitable choice of the extent of the individual
poles P.sub.1 to P.sub.3 in the direction of motion. Since maxima
as sharp as possible, i.e., narrow maxima of the curves are desired
which lead to correspondingly distinct write signals, the
longitudinal width b.sub.2 of the pole P.sub.2 is chosen
advantageously in a special embodiment of the head, substantially
smaller and preferably at most half as large as any of the
corresponding widths b.sub.1 and b.sub.3 of the adjacent poles
P.sub.1 and P.sub.3 of opposite polarity. For reasons of symmetry,
the widths b.sub.1 and b.sub.3 should in general be chosen
approximately equally large.
It is furthermore particularly advantageous if the magnetic
conduction body 16 of the magnetic head 2 is built-up from at least
two different magnetic materials which have a relative permeability
.mu..sub..tau. as large as possible, for instance, at least 1500,
and preferably at least 2000 and have in addition different
saturation magnetizations M.sub.s1 to M.sub.s3. The saturation
magnetization M.sub.s2 of the central magnet leg 6 should have a
value at least 20% and preferably at least 30% higher than the
saturation magnetizations M.sub.s1 and M.sub.s3 of the other two
magnet legs 5 and 7. Since the two outer magnet legs 5 and 7 are
generally built-up from the same material, M.sub.s1 and M.sub.s3
are then equal. Accordingly, the central magnet leg 6 consists, for
instance, of a CoZr alloy with a saturation magnetization M.sub.s2
of about 11.2 kA/cm. The two outer magnet legs 5 and 7, on the
other hand, may be made for instance, of a special permalloy alloy
(NiFe alloy rich in nickel) with a saturation magnetization M.sub.
s1 and M.sub.s3 of about 8 kA/cm. For the write function, the
central magnet leg 6 is then excited by the two oppositely
connected coil windings 19 and 20, where each of the two outer
magnet legs 5, 7 takes only about one-half of the magnetic flux of
the inner magnet leg 6. Due to the higher saturation magnetization
of the CoZr material of the central leg 6, a flux density about 40%
higher can be achieved than in the NiFe material of the outer
magnet legs 5 and 7, and the writing field strength is
advantageously increased thereby accordingly.
In addition, the outer magnet legs 5 and 7, in this special
embodiment of the magnetic head of different magnetic materials,
the cross-sectional areas thereof, carrying the magnetic flux or
their corresponding longitudinal widths b.sub.1 and b.sub.3,
respectively, can be reduced in the region of their poles P.sub.1
and P.sub.3 designated with 31 to such an extent that they are
already saturated before the central magnet leg 6 goes into
saturation. In this manner, the vertical writing field can further
be increased to advantage.
In the special magnetic head 2 according to FIGS. 1 and 2 with
materials with different saturation magnetization, it is assumed
that the three magnet legs 5 to 7 consist over their entire
vertical length of at least one layer of a material of
predetermined saturation magnetization M.sub.s1, M.sub.s2 and
M.sub.s3. Optionally, however, the magnetization conditions desired
for the write process can also be obtained if the predetermined
materials are provided only for parts of the magnet legs such as in
particular for the region 31 of the individual poles. In addition,
also materials with different saturation magnetizations M.sub.s1
and M.sub.s3 can be chosen for the two outer magnet legs 5 and
7.
A further thin-film magnetic head according to the invention which
is shown in FIG. 3 and generally designated with 32 differs from
the magnetic head 2 according to FIG. 1 substantially only by the
features that its magnet coil device is not formed by two planar
coil windings but that only a single coil winding 33 is wound
around the central magnet leg 6 of the conduction body 16 of the
magnetic head in a stacking technique known per se. According to
this technique, the current conductor parts 34 and 35 of the coil
winding are formed between the magnet legs 5 and 6, 6 and 7, the
current oonductor parts 34 and 35 of the coil winding to be
arranged there by a thin-film technique, structured and then
connected to each other to form a single coil winding 33. The
current flow directions in the current conductor parts 34 and 35,
illustrated by the current flow direction symbols, on both sides of
the central magnet leg 6, are therefore of necessity
antiparallel.
In a further embodiment of a thin-film magnetic head according to
the invention, only the end portion facing the recording medium is
shown in FIG. 4 corresponding to the view of FIG. 2. This magnetic
head, generally designated with 40, differs from the magnetic head
2 according to FIGS. 1 and 2 substantially only by a special design
of the outer magnet leg 41 and the inner magnet leg 42 of its
conduction body 43 carrying the magnetic flux, since its magnet
legs 41 and 42 can be driven into magnetic saturation at least in a
partial section 44 and 45 with an existing, relatively large write
current which is illustrated by the current flow direction symbols
shown. To this end, the outer magnet leg 41 has a correspondingly
small cross section of its material carrying the magnetic flux in
the partial section 44 so that it then acts like a magnetic barrier
for the magnetic flux which is generated by the current conductors
21 and 24, or 34 and 35 of a magnetic coil device 18 or 33 located
on both sides of the central magnet leg 46. In a similar manner, a
small cross section of its material carrying the magnetic flux is
also provided for the inner magnet leg 42 in a partial section 45.
At the pole ends P.sub.1 and P.sub.3 of these two magnet legs 41
and 42, at most a minimum magnetic flux is consequently still
provided, so that the write function is executed practically only
by the magnetic flux at the pole P.sub.2 of the central magnet leg
46. The field lines issuing at the pole P.sub.2 are designated with
47 in FIG. 4. The magnetic head 40 according to the invention
therefore writes advantageously like a single-pole head. The
vertical magnetic base field H.sub.y produced thereby which is
shown in FIG. 4 in diagram form as a function of the position in
the direction of motion of the head plotted on an x-axis then has a
pronounced very narrow maximum, by which correspondingly distinct
write singals can be generated.
According to the embodiment of the magnetic head 40 shown in FIG.
4, it was assumed that the partial section 45 of the inner magnet
leg 42 is provided with a reduced cross section by the fact that in
this leg, a corresponding recess 48 of nonmagnetic material is
provided on the side facing the substrate 3. This recess can be
developed, for instance, by an appropriate structuring of the
substrate 3. It goes without saying that a corresponding recess can
be provided also on the opposite side, i.e., on the side of the
interspace 22 formed between the inner magnet leg 42 and the
central magnet leg 46. In addition, the partial sections 44 and 45
of reduced cross section of the two magnet legs 41 and 42 may not
have only the relatively short distance assumed in FIG. 4 in the
direction of the flux return, but the partial sections can each
extend over the major part of the corresponding magnet leg.
In addition, the maximum dimension, illustrated in FIG. 4, of the
poles P.sub.1 and P.sub.3 in the direction of motion relative to
the central pole P.sub.2 is not absolutely required in the
embodiments of a double-gap magnetic head with reduced-cross
section partial sections which can be driven into magnetic
saturation by a write current. Thus, these poles can also be
included, for instance, in the partial sections with reduced cross
section, so that their longitudinal extent is then always smaller
than that of the central pole P.sub.2 .
In a further embodiment of a magnetic head according to the
invention, shown in FIG. 5, a write/read coil arrangement which can
be fabricated by a stacking technique as in the magnetic head 32
according to FIG. 3, is taken as the base. Accordingly, in this
magnetic head designated with 50, in the design of which the
magnetic head 32 according to FIG. 3 is taken as the base, the
single coil winding 52 is wound around the central magnet leg 56 of
its magnetic conduction body 53. In addition, this magnetic head 50
differs from the magnetic head 2 and 32 according to FIGS. 1 and 3,
also by the fact that its two outer magnet legs 55 and 57 each
consist of at least two magnetic layers 58, 59 and 60, 61,
respectively, with different values M.sub.s of their saturation
magnetizations. The layers 58 and 60 of the outer legs 55 and 57
which extend up to the pole ends P.sub.1 and P.sub.3 have a lower
M.sub.s value. These values designated with M'.sub.s1 and M'.sub.s3
can correspond, for instance, to the values M.sub. s1 and M.sub.s3
according to the specific embodiment according to FIG. 2 and may
optionally be also equal. Therefore, the mentioned NiFe alloy can
be chosen as the material for these layers. On the other hand, the
additional magnetic layers 59 and 61 of the two outer magnet legs
55 and 57 consist of a material with a higher value M'.sub.s2 of
the saturation magnetization which do not extend into the region of
the respective pole ends into the region designated with 62. Thus,
the mentioned CoZr alloy with the value M.sub.s2 according to FIG.
2, can be chosen for these additional layers. The central magnet
leg 56 consists, for instance, also of this material with the
saturation magnetization M'.sub.s2. It can be achieved by this
embodiment that, for the write function with a large current, the
two outer poles P.sub.1 and P.sub.3 of the mentioned NiFe alloy are
saturated quickly and the magnetic head 50 therefore operates as a
single-pole head. The unsaturated outer CoZr layers 59 and 61
thereby improve the conduction of the magnetic flux and thereby the
write sensitivity. This desired function is available also if,
according to FIG. 5, the layers 59 and 61 with the higher
saturation magnetization M'.sub.s2 are not arranged on the
respective outer side of the layers 58 and 60 with the smaller
saturation magnetization M'.sub.s1 and M'.sub.s3, but on the inside
thereof.
Besides the mentioned CoZr material for the layers having a high
saturation magnetization according to the embodiments shown in
FIGS. 2 and 5, also other materials such as FeB or FeSiRu can be
provided.
The magnetic heads according to the invention are advantageously
fabricated by a thin-layer or thin-film technique known per se. The
substrates used consist, for instance, of TiC and Al.sub.2 O.sub.3.
For building up the magnet legs, thin magnetic layers of special
NiFe alloys such as permalloy (Ni/Fe-81/19) or magnetically soft
amorphous materials, for instance, of FeB are applied by
sputtering, vapor deposition or electroplating and are separated
from each other by a nonmagnetic intermediate layer. The easy
direction of magnetization cah be induced, for instance, during the
application of the respective layer by an applied magnetic field.
In general, it is always perpendicular to the direction of the
magnetic flux in the magnetic conduction body, i.e., in the
vicinity of the magnet poles P.sub.1 to P.sub.3 substantially
parallel to the surface of the recording medium M. The grown
different layers are structured by techniques known per se such as
photolithography, plasma-, ion beam- or wet-chemical etching in
order to design the magnet legs of the head in this manner. For
fabricating the magnet coil arrangement provided for the magnet
coil device for the write and read function, a layer several .mu.m
thick of Cu or Al or Au is deposited and structured accordingly.
The individual insulating layers required for building up the
magnetic heads are omitted in the figures for reasons of
clarity.
In the foregoing specification, the invention has been described
with referenee to specific exemplary embodiments thereof. It will,
however, be evident that various modifications and changes may be
made thereunto without departing from the broader spirit and scope
of the invention as set forth in the appended claims. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than in a restrictive sense.
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